1. Field of the Invention
The present invention is directed toward an optical method and associated apparatus for determining a physical property of a hollow transparent article and, more specifically, it is directed toward such a method and system for determining the characteristic, such as wall thickness and shape, by means of multiple inspection light beams which are received by multiple detectors and processed to ascertain the desired information.
2. Description of the Prior Art
It has been known to employ optical non-contacting means to inspect hollow transparent articles by passing a light beam through the article having the light beam received by optical-electrical sensor means which convert the received light into a corresponding electrical signal which is processed by a suitable computer to compare the received signals with stored information. See, for example, U.S. Pat. No. 5,291,271.
U.S. Pat. No. 4,822,171 discloses a method and apparatus of measuring wall thickness of a transparent container wherein a scanning beam and imaging lens are employed. The system does not have the capability of determining whether the interior and exterior wall surfaces are parallel or the shape of the container. It employs vertical orientation and a single receiver.
U.S. Pat. No. 4,902,902 discloses apparatus for determining thickness of a material such as a glass plate. It employs a single beam and line-scan camera in combination with imaging lens. It not only requires the presence of an imaging lens, but also lacks the ability to make a determination of whether the wall surfaces are parallel and to make a shape determination.
U.S. Pat. No. 5,291,271 discloses a system employing a single beam, a line-scan camera in combination with an imaging lens. Laser light is employed along with container rotation.
U.S. Pat. No. 5,636,027 discloses a dual beam system having a dual line-scan camera with imaging lenses. As a result of the presence of only two receivers, it lacks the ability for determining shapes such as radii and also as a result of the required use of an imaging lens, it has positional limitations.
European Patent Application EP 0 871 007 A1 discloses a single beam and line-scan camera in combination with imaging lenses. While it discloses means for measuring container diameter, it lacks the ability to distinguish between various shapes, such as an elliptical shape and flat spot, for example.
In spite of the foregoing disclosures, there remains a very real and substantial need for an improved type of system for inspecting transparent hollow articles wherein wall thickness, parallel relationship between interior and exterior surfaces of the wall and shape may be automatically and effectively determined.
The present invention has met the hereinbefore described needs.
The method of the present invention determines a physical characteristic of a hollow transparent article by positioning the article at an inspection station, creating a scanning light beam, splitting the scanning light beam into two inspection light beams and causing the two inspection light beams to impinge on different portions of the article. A plurality of sensors are employed to receive the light reflected from the external and internal surfaces of the wall of the article and convert the same into electrical signals which are delivered to a suitable processor. The processor may be a microprocessor programmed in a manner well known to those skilled in the art. A sensor also provides initiation of a timing cycle. The times of arrival on the reflected light beams are compared by the processor from sensor to sensor and are employed in making a determination as to whether the interior surfaces are parallel to the exterior surfaces, whether the article has a particular shape and such things as wall thickness.
The method does not require the use of an imaging lens intermediate the article and the sensors. Preferred parameters regarding the inspection light beam regions of impingement, the times of arrival of the plurality of sensors and other characteristics of the information being sought are provided.
The apparatus of the present invention includes a light source, which may be a laser, for emitting a light beam which is delivered to a scanner which creates a scanning light beam which in turn by a beam splitter is converted into a pair of inspection light beams. The inspection light beams are caused to impinge on the article being inspected from generally opposed directions with a plurality of sensors receiving reflected light beams from the article being inspected and converting the same into responsive electrical signals which are emitted to the processor for determination based upon time of arrival of the reflected light beams at respective sensors to make various determinations regarding thickness and shape of the article being inspected.
It is an object of the present invention to provide an accurate, rapid, multi-beam method of inspecting hollow transparent articles to determine characteristics such as wall thickness and shape.
It is a further object of the present invention to provide such a system wherein a plurality of sensors receive reflected beams and permits a processor, based upon relative timing of receipt of the same, to make such determinations through comparisons.
It is yet another object of the present invention to provide such a system which is suitable for inspecting transparent glass or plastic containers.
It is a further object of the present invention to provide such a system which does not require the use of positional limiting imaging lenses.
It is a further object of the present invention to provide such a system which is adapted to determine radii and wall thickness of transparent containers.
These and other objects of the invention will be more fully understood from the following detailed description of the invention on reference to the illustrations appended hereto.